At a time when many repentant leftists are proclaiming Marxism incapable of explaining the new phenomena of this last quarter of the twentieth century, Ernest Mandel reminds us in The Place of Marxism in History that Marxism drew from its very inception on the advances of all the social sciences and emancipation movements of its time. In a survey of the multiple sources of Marx and Engels’ theory, he identifies the specific contribution of the two friends in the various disciplines to which they applied themselves: philosophy, political economy, social history, revolutionary organisation, self-organisation of the working class, emancipation movements, internationalism. Concluding that Marxism “constantly learns from perpetually changing reality” and that it is the conscious expression of the real movement of workers towards self-emancipation, Mandel propose a formula which provides for a dialectical interaction between innovation and the verification of established tenets. This text is based on a series of lectures given at the International Institute for Research and Education.